A system for measuring substance concentrations in solutions on the basis of a fluorescence measurement is known from EP 2 295 953 A1, in which an optical sensor is releasably connected to a structurally compact measuring unit. The optical sensor includes a sensor head, which is inseparably connected to a housing, which contains a signal evaluation electronics. The housing, moreover, has a light source, which radiates an excitation radiation into a liquid to be examined. With this excitation radiation, a sensitive element, which is arranged in the medium to be examined and is contained in the sensor head, is excited. This sensitive element radiates light back as a function of the substance concentration.
The fluorescent radiation radiated back by the sensitive element is received by a detector unit and forwarded to the sensor electronics. Depending on the properties of the sensitive element, the optical sensor reacts to different particle concentrations with different light intensities, frequencies or decay curves.
A cap for use with optical sensors is known from WO 2007/014539 A1, wherein the cap is embodied replaceably for a connection piece, which contains optical or optoelectronic components. The sensitive element, which is used for the measurement of physical or chemical parameters, is arranged in the cap in such case. In order to assure that the right sensitive element is always secured to the connection piece that fits thereto, the cap and the connection piece are protected against mix-ups by complementary coding options.
It is disadvantageous in these arrangements that an individual sensor for each measurement parameter must be developed and manufactured, which leads to a high production effort.